In the manufacturing of integrated circuits, contact plugs are used for connecting to the source and drain regions and the gates of transistors. The source/drain contact plugs are typically connected to source/drain silicide regions, whose formation process includes forming contact openings in an inter-layer dielectric, depositing a metal layer extending into the contact openings, and then performing an anneal to react the metal layer with the silicon/germanium of the source/drain regions. The source/drain contact plugs are then formed in the contact openings.
In conventional processes for forming the contact openings, the positions of the contact openings are defined by titanium nitride masks, and a photo resist is formed over the titanium nitride masks. The photo resist and the titanium nitride masks are in combination used as an etching mask to etch the inter-layer dielectric and to form contact openings.